Note: In many fishes the vertebr[ae] are simple cartilaginous
disks or short cylinders, but in the higher vertebrates
they are composed of many parts, and the vertebr[ae] in
different portions of the same column vary very
greatly. A well-developed vertebra usually consists of
a more or less cylindrical and solid body, or centrum,
which is surmounted dorsally by an arch, leaving an
opening which forms a part of the canal containing the
spinal cord. From this dorsal, or neural, arch spring
various processes, or apophyses, which have received
special names: a dorsal, or neural, spine, spinous
process, or neurapophysis, on the middle of the arch;
two anterior and two posterior articular processes, or
zygapophyses; and one or two transverse processes on
each side. In those vertebr[ae] which bear
well-developed ribs, a tubercle near the end of the rib
articulates at a tubercular facet on the transverse
process (diapophysis), while the end, or head, of the
rib articulates at a more ventral capitular facet which
is sometimes developed into a second, or ventral,
transverse process (parapophysis). In vertebrates with
well-developed hind limbs, the spinal column is divided
into five regions in each of which the vertebr[ae] are
specially designated: those vertebr[ae] in front of, or
anterior to, the first vertebra which bears ribs
connected with the sternum are cervical; all those
which bear ribs and are back of the cervicals are
dorsal; the one or more directly supporting the pelvis
are sacral and form the sacrum; those between the
sacral and dorsal are lumbar; and all those back of the
sacral are caudal, or coccygeal. In man there are seven
cervical vertebr[ae], twelve dorsal, five lumbar, five
sacral, and usually four, but sometimes five and rarely
three, coccygeal.
2. (Zo["o]l.) One of the central ossicles in each joint of
the arms of an ophiuran.